Decide if the capacity of the router need to be changed. Will be invoked when `isTimeForResize` returns true and no other resize is in progress. Return the number of routees to add or remove. Negative value will remove that number of routees. Positive value will add that number of routess. 0 will not change the routees. This method is invoked only in the context of the Router actor.

public abstract int Resize(
	IEnumerable<Routee> currentRoutees
)

abstract Resize : 
        currentRoutees : IEnumerable<Routee> -> int